Traditionally, there's an amount of melodrama (clear good/bad), a femme fatale (a woman who brings about the doom of the man), a distinct visual style, etc. Or so I was told in a couple of film classes.
I would add a general attitude of cynicalism, certainly on the part of the lead character.
I don't know if strictly speaking the film would have to be in black and white, but visually it should be "dark" and muted.
Raining the whole time (Blade Runner) helps.
what about a good naive lead character (man) that got seduced by a femme fatal? the 2 attitudes contradicts each other no?